Process for manufacturing superphosphates



Jan. 12, 1943. w. H. WAGGAMAN PROCESS FOR MANUFACTURING SUPERPHOSPHATES Filed Aug. 29, 1941 Patented Jan. 12, 19 we i'rEn STATE pplication Au 29,

s PATENT I orrica 1 G SP'IES timore, Md.

erial No. alias-as 3 Claims. (mil- 40) This application is a continuation in part of myco-pending application,- Serial No.373,829,filed January 9, 1941, and relates to the production of fertilizers and more particularly 'tothe manu-' facture' of superphosphates by the acidulation' of phosphate rock with. sulphuric acid.

The primary object of the invention is to provide a process of producing superphosphates more chamber where. the chemical actionscontinue and the product sets up as a porous cake. In, order to factilitate the reactions, drive oficertain gaseous compounds of fluorine, evaporate free water from the mass, and thus obtain a relatively dry product, it is customary to employ rather concentrated sulphuric acid, and also to heat this acid to a temperature ranging from 125 to 140 economically than has heretofore been possible.

Another object of the invention is to provide a method of acidulating phosphate rock with sulphuricacid-by which a reduction of the acidrock ratio below that normally employed is made I feasible without sacrifice in the conversion of the insoluble phosphates into an available form. Another object of the invention is to provide a method of processing phosphate rock by which the porous or cellular mass produced on the initial acidulation of the rock is subsequently rendered more dense and the conversion of the residual rock into an availableform is promoted.

A further object of the invention is to provide I a process ofproducing superphosphates whereby a product is obtained which is superior in physical andv chemical properties to the superphosphatesmanufactured in the usual manner.

A still further object of the invention is to provide a process of manufacturing superphosphates I from' phosphate rock whereby a product is ob tained which has less free acid and hence is less corrosive of handling equipment and the containers in which it is stored and shipped than the superphosphates nowin use.

An additional object of theinvention is to .provide a process of manufacturing superphos'phates from phosphate rockwhereby adense dry granu- The resultant product consists chiefly of a mixture of monocalcium phosphate, anhydrous calcium sulphate (anhydrite), some free acid and from ii to 12 percentpf free moisture. After ouring, the free acid and moisture are reduced, due

to both drying out and further chemical reactions.

lar product is'obtained which, because of its I physical and chemical nature, has little tendency to set' when stored alone or mixed with other fertilizer materials, thus enabling the superphosphate to flow freely through the fertilizer distributing machine-and be uniformly and readily distributed over a field. I I e I These and other objects will appear hereinafter rein? the detailed description of the'invention and .-be particularly pointed out in the appended;

claims.

' Throughout the drawing and specification like parts are designated by like reference characters.

. In the drawing: I

In order to drive off a still centage of P205 in the final product, certain manufacturers of superphosphate dry this product in a rotary cylinder heated by a direct flame or indirectly with steam. Due to the rotary motion of thecylindrical drier, the product thus formed is in the form of porous-granules or pellets.

The ratio-of sulphuricbacid to finely ground phosphate rock ordinary employed varies somewhataccording to the nature of the phosphate rock and the concentration of theacid employed,

but the average acid-rock ratio in terms of 55?. B.

acid is-in the neighborhood of 86/100 where Florida pebble phosphate is employed, and about 89/100 where Tennessee brown rock phosphate is'used.

I 'It has heretofore been believed that unless the ratio of acid to the rock dust employed is rela- Figure 1 is a side elevational view of amachine forpressing phosphates, and Figure 2 is an end elevation viewof the machine shown in Figure 1.

In the ordinary method of manufacturing superphosphate, finely groimdphosphate rock and sulphuric acid are intimately mixed in some standard type (if mechanical mixing device equipped with stirring arms and then discharged as a slurry or'muddy mass into a den or reaction to and b ll winst ix mass to part l y ure tivelyhigh substantiallyjcomplete conversion of the P205 into an available form was not obtained.

Thistheory was based upon the porous nature of'the product brought'about by theevolution of I the gaseous products and partiallydue to the limited quantity of activating acid. in a liquid phase present in the mass when concentrated acid is employed. 1 havei 'discovered, however, that it is possible to obtain-substantially complete conversion of the phosphaterock dust into available P205 where the ratio of acidto-rock dust is ma- -.terially reduced from that commonly used in this; I Q

connection. v I I a By utilizing a very much lower ratio between rock dust and acid than is commonly employed greaterpropo'rtion of the free moisture and to thus increase the peror harden in a den and by then subjecting the cured or "set up" denned product to further mixing and pressure the ultimate product of my process, besides possessing highly desirable mechanical properties, shows by analysis to contain as much available P205 as has been obtained in the past with the higher ratio between acid and rock dust. I

In carrying out my invention I have foun that I may utilize sulphuric acid of a-concentration varying between 50 B. and 56 B. A slightly higher percentage of available P205 is obtained by utilizing sulphuric acid having a concentrationof approximately 53 B. When acid of this concentration is mixed with phosphate rock dust in the general ratio of approximately 79.5 acid to 100 parts rock dust, which, measured on the basis of 55 B. acid, gives a ratio of 76 to 106, I have found that if I permit the mixed product to cure or partially cure or set up" in a den and then subject the set up" product to a further mixing and to a high degree of pressure either with or without the, application of heat,

the resultant mass compares favorably with, so far as available P205 is concerned, the best product produced by any other method.

. It is to be understood, however, that the inthe den a substantially solid mass of material.

The denned massis rigid but, owing to the evolution of gases is, in fact, a cellular mass. The denned mass, when this stage is reached, is then excavated by any desired method and the product, 4

after passing through the hopper l, shown in the accompanying drawings, flows to the space 2 between the periphery of the metallic rolls 3'and 4. The rolls 3 and 4 .are preferably rotatably mounted, by means of the shafts 5 and 6, in suitable fixed bearings 5; The distance between the centers of rotation of the rolls 3 and 4 may be varied by any desirable means, as for instance by screw 6, but preferably the contiguous surfaces of the rolls are spaced apart one-fourth of an inch.

As will be noted from the drawing, both the shafts 5 and 8 of the rolls 3 and 4 are provided v with an opening I extending within the hollow roller by means of which steam may be introduced within the rollers to heat the surfaces thereof in heres to the surface of the roll 4. The speed of vention is not limitedto the particular concentration of acid spec ified or' to a definite ratio between acid and rock dust. Phosphate rock from different sources varies in chemical composition and in other properties and it is therefore desirable to adjust the acid and rock dust ratio as well as the 'acid concentration so as to compensate for .the physical and chemical nature of the rock dust to be treated.

The actual quantity of HzSOa employed per unit ofphosphate rock treated will vary according to the composition and fineness of the rockdust, but it has been found that the amount of acid required to convert the P205 of the rock into an available form is from 8 to 10 percent. below that normally employed. As a specific example, when 'using Florida pebble phosphate, I employ acid rock ratios of from 75/100 to 78/100 instead of the average acid rock ration of 86/100 as ordinarily used, these ratios being calculated on the basis of 55 B. acid, and obtain fully as good conversions of the insoluble P205 into an available form.

In my co-pending application I have pointed out that to obtain the acid economy set forth therein it was desirable, if not absolutely neces-- sary, to maintain the temperature of the mass during the mixing-period at a predetermined point, preferably not greater than the boilingpoint of water, but I have since found that the cooling of the mixed mass, while beneficial, is

not essential, in connection with the use of acid of concentrations running from 53 BQto 56 B., in order to obtainithe same amount of conversion of the rock dust into available P205 as is commonly obtained by-utilizing a higherratio of acid to rock dust.

time period. It is then discharged into a-den of any desired type and the productallowed to the arrows, and the roll 4 in a counter-clockwise direction. The material in the hopper- I, by the difference in the speed of rotation of the rolls, is-caused to be tumbled and mixed before passing between the contiguous surface of the rolls, at which point it is compressed so as practically to eliminate the cellular condition of the denned mass and to cause the product, after passing be- .tween the rolls, to be hard and dense.

Adjacent the surface of the roll 4 I mount on a shaft 8 a series of cutters 9, and interposed between each pair of adjacent cutters a thimble ID. The cutters 9 and the thimbles ID are freely rotatable on the shaft 8 and the edges of the cutters are preferably tangent to the periphery of the roll 4. By this means the compressed layer of phosphate -material is formed into a series of strips running circumferentially of the roll and at a point spaced from he shaft 8 in the direction of rotation of the 521131 4 I provide a pivoted scraper .bar II by me of which the strips face of the roll and deposited in the hopper l2 from which they may be conveyed either to storage or .to grinding orcrushing rolls so as to form the phosphate into a dense granular mass, the

granules of which are substantially uniform in cross section.

The rolls 3 and4 are preferably spaced,'as stated. above, so that their respective peripheries are so positioned as to cause the material to be greatly compressed as the same is forced between the rolls. The spacing between the rolls largely depends upon the character and consistency of the material and also upon the amount of product set or cure or harden until there is obtained in '75 which it is desired to obtain from;the rollss It will be obvious that by changing the diameters and/or length of the roll, production can be increased or decreased and a like increase or decrease may be obtained by increasing'or decreasing the rate of revolution. a

The rolls are or may be driven by suitable gearing as shown, the respective gears I4 and I4 being splined to the shafts 5 and 8, respectively, and driven by the intermeshing gears 85.

The scraper bar H is preferably provided with a curved surface ll so that the compressed strips of superphosphate, as removed from the surface of the roll 6, will be directed onto the guide plate it and thence into the hopper it.

Any kneading or further mixing of the denned product, which is immediately followed by the dust than is employed in my process.

It has also been found that the product pro- .duced by the scrapers from the roll can be immediately dried without adversely efiecting the resulting product, whereas unprocessed superphosphate is detrimentally afiected to a. high degree by being submitted to elevated temperatures. The following table shows conclusively the beneficial effect of compressing the cured or partially cured denned product. The superphosphate, after being formed from mixing the run of the mill rock and -55" B. sulphuric acid with an acid ratio of 80 to 100 gave" the following results:

Time of curing (beiore R1088.

Total curing period Insol. Avail. P205 5 Total P20:

Conver- Sample Nos. Sign Average of 4 samples (91A, 9lA1, 91A,, Days Days Per cent Per cent Per cent Per cent QIAJ) 2 8 21.70 1.26 20.44 94.2

Average of 12 samples (83B, 83 a, 8482 1 Not pressed. Pressed.

- 'The following table shows the efiect of heating compressed and-unprocessed superphosphates:

As a result or my improved I In this table it will be noted that both products were'cured'in the den four days and that the.

same identical materials were used. One product is compressed by being forced betvi "en the surfaces of rolls in accordance with my invention and the other is not treated in accordance. with my process.

untreated superphosphate is only90.90%, where- The total conversion in the as in the compressed .product the total conversion is 96%. I

-With an acid-rock ratio of to 100, as shown in the last bracket of this table, there is a difierenceof slightly more than 5% conversion in the compressed product over the untreated product. It-will be noted from an inspection of the drawings and from the foregoing description that my improved process does not require come plex machinery nor necessitate the use or combined'drying and conveying cylinders heretofore consideredessential in the production of superphosphate of similar nature. therefore, by employing the method herein set forth; a saving to the manufacturers not only in the cost of machinery but a very marked saving in the amount of acid used. It is dimcultto measurein actual dollars and cents the extent of saving since acid costs are continually mounting as more and more sulphuric acid is being utilized for directdefense projects. Taking sulphuric acid at the market cost prior to 1 the present emergency andleven considering the amortization of the cost of the necessary roller equipment'and the operating means therefor, the

saving runs to from tento sixteen cents per'ton. All increases in theprices of sulphuric acid over the base price increase this saving. Were the phosphate industry limited in output the saving mentioned would not perhaps be of vital im- 'portance but where the normal annual output of the phosphate industry exceeds four million tons of commercial superphosphate it will be obvious that the potential saving by the use of this new process, if utilized by the entire industry, would amount to approximately half million dollars a year without any loss in the availability for agricultural use for the superph'osphate sold.

, ving thus described my invention 'what I 7 claim as new and desire to secure by Letters Patent is:

1. A method of. phate in a denned sulphuric acid of approximately 53 B. with incresing the available phosphosphate rock dust in the proportion of 76/ 1 on a basis of 55 B. acid, said method comprising subjecting the set up denned material to a further mixing and pressure by depositing said material between fixed positioned rolls, one of which rotates at a higher R. P. M. than the other, and finally removing the pressed material from the surface of oneof said rolls.

2. A method of-increasing the available phosphate in a cured material formed by mixing sulphuric acid of approximately 53 Bewith phosphate rock dust in the proportion-of 79/100, said method including the denning of said mixed product, allowing the denned material to ,set up, subjecting the said set up denned material to further mixing and pressure by depositing said material between metallic rolls, one of which rotates at a higher R. P. M. than the other, and finally removing the compressed material from said rolls.

3. A method of increasing the availablephos There is,-

pr duct formed by mixin phate in a cured materiaiiormed'bymixingsulphuric acid of approximately 53 B. with phos-- material between metallic' rolls, one of which rotates at a higher R. P. M. than the other, heating the surface of one of said rolls to dry the compressed material, and finally removing said compressed material from the surface of said heated roll. 7

WIILIAM H. 'WAGGAMAN. 

